Compositions containing two or more different metals have found use in several areas. Sometimes the compositions themselves can act as catalysts; more often, they behave as catalyst precursors, being transformed into active catalysts by reduction to give alloys or thin films or by oxidation (calcination) to give mixed-metal oxides. These oxides may behave as ceramics as well as catalysts. Often, these mixed-metal compositions are simple mixtures of single-metal compounds. Reduction or calcination of such mixtures can give non-homogeneous products because of incomplete mixing of the compounds, resulting in monometallic domains. When possible, it is advantageous to use as precursors unique compounds containing the desired metal ratio, because the metals will be intimately mixed, even at the molecular level.
Mixtures of metals have other uses, as well. For example, iron, zinc, and magnesium are found in agricultural nutrient formulations, whereas iron, zinc, chromium, cobalt, and calcium are found in animal and human dietary supplements. Routinely, these sorts of formulations contain mixtures of compounds, each compound containing one of the desired metals. To reduce the amount of ancillary organic material in these formulations, it can be advantageous to provide two or more metals in a single compound, thereby increasing the percentage of metals vis-a-vis the organic ligands.
Iron chelates are a class of compounds that have found use in natural gas treating, photographic bleaching, fertilizers, and dietary supplements. Routinely, said iron chelates are used as ammonium or alkali metal salts. In such cases, the alkali metal or ammonium ion provides charge balance but otherwise imparts no useful properties to the iron chelate. For example, sodium ferric ethylenediaminetetraacetate (NaFeEDTA) has been used for iron fortification in foods. The iron provided is beneficial, but the sodium is possibly hazardous to those people requiring a low-sodium diet. On the other hand, iron chelate complexes with calcium can potentially be used to provide the dietary benefits of both metals.
Because of its tetravalent nature, ethylenediamine-tetraacetic acid (EDTA) can conceivably combine with a divalent and a trivalent metal to form complexes of the general formula M(II)M'(III)EDTA(OH).xH.sub.2 O. To our knowledge no such mixed-metal complexes of EDTA have been reported in the literature.
The calcium salt of the ferric chelate of a similar ligand, hydroxyethylethylenediaminetriacetate (HEDTA), was reported as an amorphous, red solid (without analytical data) by Schugar, et al. in J. Amer. Chem. Soc., 89, 3712 (1967).
There is clearly a need for transition metal chelate, particularly iron chelate, complexes with calcium which can be used to provide the dietary benefits of both metals.
The present invention offers such transition metal chelate complexes with calcium and a process for their preparation.